Method of reducing barrel wear



United States Patent 3,256,818 METHOD OF REDUCING BARREL WEAR Bernhard Berghaus, Zurich, Switzerland Filed Mar. 23, 1964, Ser. No. 354,108 9 Claims. (Cl. 102-93) The present application is a continuation-in-part of my application Serial No. 732,605, filed May 2, 1958 now issued on Apr. 28, 1964, as Patent No. 3,130,671.

The present invention relates to an improved driving band for projectiles whereby reduction of wear and increased serviceable life of the inner barrel due to passage of said projectiles thereth-rough is obtained especially when used with barrels, the inner surface layer of which has been enriched with a foreign substance.

In present day firearm-s the inner wall of the barrels is subject to very high stresses and it reaches a temperature, particularly in automatic quick-firing guns, which is near the melting point of the barrel material. This results in a measurable quantity of fused or vaporized material leaving the barrel with each projectile during firing. In so far as such material comes from the driving band of the projectile-s, no drawbacks need be anticipated. But, if the material ejected stems from the inner barrel wall, this definitely involves a highly undesirable wear of the barrel. Weighing the barrels of quick-firing guns prior and subsequent to firing revealed weight losses of up to 100 grns.

Recent developments in firearm-technology, mainly the increase in the use of firearms, along with the transition to more powerful explosives has caused the life of barrels to be increasingly shortened so that the individual barrel or entire gun must be replaced after a comparatively short service life.

On the discharge of a projectile, provided with a driving band from a gun barrel, the driving band after a short flight of the projectile is pressed into the rifling grooves in the inner wall of the barrel and deformed in such manner that the grooves press into the guiding ring and-thereby the rifling of the grooves, in the direction of the barrel length, is applied to the driving band and thereby to the projectile. By reason of the friction and deforming of the driving band in the grooves, there is produced a very high temperature in the inner surface between the driving band and the groove or inner wall whereby for an increment of the distance moved by the projectile AS a definite amount of energy AW is converted into heat. Since the conduction away of heat during the relatively short time of the passage of the projectile through the barrel is practically neglilible, the

layer temperature T rises almost exactly as the flight differential AS of the projectile, to a temperature differential AT corresponding to the energy applied AW until one of the two materials forming a limiting layer has reached its melting point. From this point on the material melts and thereby uses up the flowing energy supply AW as heat of fusion, so that the limiting layer temperature from this point on remains somewhat constant and equal to the melting temperature of that one of the two materials which has the lower melting temperature. In consequence, the melting temperature of the other material is never reached so that only the material of lower melting point suffers any loss of weight. It is apparent that the temperature at points of the inner barrel subject to the greatest stress rises above the melting point during firing, at least in a thin surface layer, so that the inner wall is melted and vaporized at these points.

It would at first glance appear obvious to increase the wear and resistance of such barrel-s by raising the melting point of the barrel or at least of the inner wall. However,

this is not possible since structural strength considerations dictate that alloy steels be utilized for barrels and the surface zones of the inner barrel are generally treated by being enriched with foreign substances, e.g. by hard nitriding. However, hardness and strength on one hand and melting point on the other do not increase in direct proportion. The alloying elements :and nitrogen, although added to a pure metal to effect aninorease in hardness, simultaneously decrease the melting point of the resulting alloy which is the useful case of any mixture having a lower melting point and either of the component elements.

Therefore, it is an object of the present invent-ion to obviate the disadvantages attendant in the lowering of the melting point of the inner surface layer of a gun barrel.

A further object of the present invention is to provide means of reducing wear and increasing service life of gun barrels.

Another object is to provide a method of treating the guiding portions of projectiles so as to make said portions sacrifice material in preference to the gun barrel on repeated firing of the firearm.

A still further object of the present invention is the provision of novel and improved projectile driving band-s whereby deposits of material in the gun barrel are elimi: nated.

Yet another object of the present invention is to provide a projectile driving band, which, on firing, 'evol'ves a substance that replenishes any depletion of the same substance from the inner surface of the barrel.

Still another object is the provision of 'microporous enriched driving bands.

These objects and many of the attendant advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description and schematic drawings of an apparatus :for carrying out the method of the present invention and the article produced by said method and wherein FIG. 1 is a schematic representation of an apparatus for conducting the first step of the method;

FIG. 2 is a block representation of the process step; and

FIG. 3 is a fragmentary cross-sectional view of the article produced by the method of the invention.

The method of the present invention resides in adjusting the melting point of at least the guiding portions of the projectile to near or below that of the inner barre. wall. In tests conducted with projectiles having driving bands with melting points at least substantially adjusted to the melting point of the inner barrel or below that value, a reduction in wear was observed in every case. Apparently, a certain quantity of fused and vaporized material is necessary-for-the passage of the projectiles through such firearm barrels. If the melting point of at least the guiding portions of the projectile is lower than the melting point of the inner barrel wall, the fused material is largely supplied by these portions and not by the inner barrel wall. This protection of the inner barrel wall is responsible for the improvement in the resistance to wear and extension of the service life of the barrel.

Of course, it is not necessary that the melting point of the guide portions be adjusted accurately to the melting point of the driving portions of the inner barrel wall since an approximate adjustment is sufficient to result in a marked improvement of useful life of the barrel.

A particularly advantageous manner of adjusting the melting point of the guide portions of the projectile to that of an inner barrel wall is by difi'using a suitable foreign substance into said portion of the projectile. By way of specific example, if the steel driving bands of.

, bardment.

steel projectiles are annealed and simultaneously enriched with nitrogen, a substantial prolongation of the life of the nitrided steel gun barrels firing such projectiles is obtained.

The arrangement of apparatus shown in FIG. 1 is suitable for such purpose. Specifically, an evacuable, coolable, double walled gas discharge vessel 1, is provided with a removable lid 2. Disposed therein is metallic supporting plate 3 which is mounted on insulators 4 and carries resilient metal pins 5 adapted to have steel pro jectiles 6 slipped thereon. Arranged parallel with the supporting plate 3 and conductively connectd therewith is a metallic orifice plate 7 arranged in a plane with the driving bands 8 of the projectiles 6 and provided with circular holes 9 through which the projectiles 6 project. The thickness of the orifice plate 7 is such as to cause the inner side of the holes 9 to register with the two driving bands 8. The inner side of the holes 9 must enclose the driving bands 8 concentrically and form an annular gap with them which is of the same width throughout.

The supporting plate 3 and the orifice plate 7 are connected with the negative pole of the pair of terminals 11 via an insulated voltage lead-in 10, while the positive connection is effected with the metallic discharge vessel 1. In the discharge vessel 1, '2 suitable means (not shown) are provided to .produce a gas atmosphere comprising 30% N and 70% H at a pressure of 5 to mm. Hg, and to maintain it during operation. After completion of a starting cycle, a glow discharge is produced at a voltage of 400 to 500 volts between the discharge vessel 1 and the projectiles 6 and on the orifice plate 7 connected to the same voltage. This glow discharge produces a particularly elevated energy concentration of 0.1 to 10 watts/cm. on the surface of the driving bands 8 between the said bands and the inner wall of the holes 9 if a suitable width of the annular gap is maintained. This operative condition is termed hollowcathode effect and results in a soft nitriding of the driving bands. A more detailed description of this procedure is given in Swiss Patent No. 314,340. Under these conditions the driving bands 8 reach the desired glow temperature within a short space of time, e.g. 0.5 to 2 minutes and are enriched with nitrogen by ion bom- The high energy density in the annular gap insures a comparatively rapid diffusion of atomic nitrogen into the driving bands so that the depth of penetration is obtained after annealing and the treatment can be discontinued. The simultaneous enrichment and annealing treatment can be effected in only a few minutes as in the present example or may be extended without disadvantage for hours.

Within the relatively short period of treatment the temperature of the other portions of projectiles 6 has been increased so slightly as to result in no loss of strength in these portions. This treatment, though described with reference to nitrogen is adaptable to any substance which diffuses into the metal surface to adjust the melting point thereof, other suitable substances being phosphorous, sulfur, either in elementary form or in the form of suitable compounds. Other gases such as hydrogen, oxygen and even the rare gases can be diffused into the metal by the above described method.

The substances to be added to the surface of the guiding portion need not be obtained from the gaseous atmosp here in the discharge vessel, other procedures being suitable. By way of example, a suitable substance may be vaporized in the discharge vessel and mixed with the gas atmosphere or a mist of particles of such material may be supplied into the discharge vessel. Alternatively, the known processes of cathode atomization or are dusting may be employed to mix the foreign particles with the gas atmosphere.

The above described electric discharge treatment is preferred because the piece is simultaneously bombarded with ions and heat treated. However, the present invention is not limited to that method and enrichment of the driving band projectile may also be affected by diffusion of the substance into the surface in a heated furnace or by immersion of the guiding portions of the projectile in a fused melt containing said foreign substance tobe diffused.

When the added substances such as the nitrogen gas of the example have been diffused into the surfac so called solid solutions are formed comprising chemical and physical combinations of metal and gas. Said solid solutions under the extreme pressure conditions encountered during firing result in a reduction of the melting point of steel driving bands to a value corresponding approximately to the melting point of nitrided steel barrel walls. The described treatment is not limited to steel parts but may be performed on non-ferrous metals and alloys. The duration of the treatment and amount of diffused substance to suitably lower the melting point varies from metal to metal. The method is particularly influential in reducing the melting point of very hard metallic materials by diffusing a substance into the surface thereof.

However, the adjustment of the melting point of the driving bands to that of the inner barrel wall has resulted in a certain condiiton which is obviated by the following modified embodiment of the invention: During tests performed with projectiles having their melting points reduced due to enrichment with substances, the inner wall was found to be covered with a thin layer of metal obviously transferred from the driving bands to the barrel wall during firing. In some cases and esspecially after prolonged use of such a barrel, the thin layer of deposit tends to form into welded beads on some parts of the inner wall. Thus the inside surface may become welded to the driving band and the accumulation may proceed to such a degree that portions of the welded surface break loose and become redeposited in the upper portion of the inside barrel.

As illustrated in FIGURES 2 and 3, it has now been discovered that these described effects can be obviated by providing said lower melting guiding portions 8a of the projectile 6 with a very thin coating 12 of a higher melting, more resistant to wear metal which is preferably a non-ferrous metal. Chromium has been found most suitable with nickel and cobalt being other specific examples of such metals. This combination of substrate and thin metal film results in the driving band having properties not obtainable from the use of either metal alone.

The ideal driving band should be soft and readily deformable and have a low modulus of rigidity and a high melting point. The deformability of soft nitrided metal rings is satisfactory but the melting point is too low. High melting metals such as chromium, nickel and cobalt are difiicult or impossible to deform. But, according to this embodiment of the invention, the thin coating of high melting chromium applied to the readily deformable low melting nitrided steel base results in driving bands having properties not heretofore obtainable viz. ready deformability but higher resistance to wear as evidenced by absence of metal deposits on the inside barrel after firing. However, the mechanical strength of the driving bands provided with such a skin is not markedly altered, being substantially the same as before the treatment. The very thin skin follows all the deformations of the rifiing of the barrel being too thin to cause any appreciable contribution to the mechanical strength of the final product. The resistance of the skin to wear is much higher than that of the surface without such a skin and the thickness need only be sufficient to protect the surface during one passage of the projectile through the barrel. The coating may be applied in any conventional manner such as by electrolytic deposition, deposition by decomposing vaporizable metal compounds or by dip coating.

'aration of enriched microporous driving bands.

v The coated enriched driving band of the present invention is extremely suitable for use with the hard nitrided gun barrels since on the creation of the first unit of fI'lC- tional energy, the limiting temperature will still be that of the lower melting enriched guiding band substrate, theenergy being transmitted through the very thin metal coating layer. A further feature of the invention resides in the pre In the treatment disclosed in'reference to the hollow cathode glow discharge, the surface structure is altered by material migration of dissolved minute particles when said surfaces are not heated to annealing temperature. It is not precisely known Whether the metal particles are dissolved out of the crystal structure due to vaporization at the point of impingement of individual ions or due to direct shock release. In any case, experiments reveal migration of material. But, at the same time, metal is also returned to the surface since the gas atmosphere is intermingled with the metal particles removed from thesurface of the work or from the counter electrode and such particles being electrically charged in the glow chamber are accelerated .as well as by adjustment of the pressure in the discharge 'vessel and by the type and polarity of voltage utilized. The conditions of the discharge are so selected that material removal is preponderant. Under these conditions the surface of the Work after maintaining the glow discharge for suflicient period of time which can be .only a few minutes as in the specifically described example or again may be several hours, is transformed into a metal body having a surface displaying a highly uniform microporosity extending into the piece for molecular distances. At the same time, the surface zone has a strength not significantly inferior to that of the original unaltered metal layer. The microporous layer becomes greatlyenriched with the gas present in the discharge vessel and maintains this gas under atmospheric conditions after completion of the treatment. The surface is enriched with gas in two respects. On the one hand, nitrogen which has been diffused therein is dissolved in the metal layer in the form of a solid solution. On the other hand, gaseous components are physically enclosed in the microporous surface layer. Under the pressure and temperature conditions prevailing during firing both the enclosed gas and solid solutions thereof contribute to the supply of lubricant gas layer between the engaging metal surfaces. The enclosed gas of the driving bands is likely to be initially effective at the outset in maintaining said gas film layer while the substantially deeper zones bearing solid solutions of the gas contribute to the supply of the gas as deformation begins. It is believed that the improvement in the life of gun barrels is the result of the simultaneous formation of a gaseous lubricant film between the surfaces in engagement. It has been previously known that a gas layer between the metal surfaces of firearm barrels and projectiles sliding one on another at a high pressure per unit area can substantially reduce friction. The gaseous lubricant film of the present invention is not supplied to the contacting surfaces from outside sources but is provided by vaporization of the gas generating materials from the surfaces in engagement or by the evolution of gaseous substances dissolved in the metal or combined with the metal surface. Of course, this is only possible under high surface pressure conditions.

Standard unprepared sliding surfaces cannot maintain a gaseous lubricant film for any length of time since a certain gas loss by diffusion into the associated surface and by the leakage from the edges of the sliding surface portions is inevitable. As projectiles provided with driving bands nitrided in conventional baths or furnaces are fired from standard, i.e. unnitrided barrels, the driving bands do supply a gas film while the barrels are cold but during rapid fire this advantageous film cannot be maintained. Apparently, the heated inner barrel wall absorbs the gases emerging from the driving bands far too rapidly for a lubricating gas film to be maintained.

in gun barrels having their inner walls enrichced with nitrogen during an electric glow discharge, the surface portions engaged by the projectile can initially supply the quantity of gas required for the formation of lubricant gas films. During firing therethrough of standard projectiles provided with unnitrided driving bands, a certain quantity of gas is lost with each projectile and thus results a detrimental reduction of theability to form a gaseous lubricant film.

However, with the present method both the gun barrel and the guiding portions of the projectile are each enriched with a suitable melting point reducing, gas releasing substance. A test made with firearms with such a barrel and projectile combination showed that the life of the gun barrel was far superior to that of unnitrided gunbarrels with nitrided driving band projectiles or nitrided gun barrels with unnitrided driving band projectiles. The gas layer formed from the heat and pressure generated by frictionalforces is supplied by both the inner barrel wall and the driving bands. Therefore, when the driving bands become heated during passage through the barrel when each single round is fired, the reduction of gas generating substances contained in-the inner barrel wall is largely prevented since the evolution of these substances from the driving bands provides a sufficient concentration and presssure to cause the same to be rediffused into the heated inner barrel. It is thus preferred that both surfaces be enriched with the same gas generating substances. However, different substances may be employed provided that the projectile portions supply those gaseous components with which the inner'barrel has previously been enriched.

Furthermore, 'it is important that the concentrationof the gas-generating substances enriched in the two metal surfaces be adapted to one another. As gun barrels must advantageously be nitrided in an electric gas or glow discharge in order to obtain a hardened but ductile and shatterproof innersurface, itis recommended to enrich the entire outside of the projectile or at least the projectile portions designed to contact the said inner wall in an ionized gas atmosphere with the same gas-generating substances although the. present method is not limited to such a treatment of the projectiles.

Depending on the foreign substances concentrated in the inner barrel wall and apart from the above-mentioned solid nitrogen-metal solutions, many other substances are suitable to supply gas. By way of example, the projectile portions can be enriched withv sulfur either in elementary form, dissolved in the metal concerned as a. solid solution, or in the form of suitable compounds. Such substances evaporate under the extreme pressures and temperatures prevailing and form the lubricant gas layer. Finally, other gases, such as hydrogen, oxygen, and, under certain conditions, rare gases may be concentrated in the metal surfaces subject to friction so that they may contribute to the formation of lubricant gas layers in order to avoid a reduction of the said substances in the inner barrel wall.

It may also be pointed out that the lubricant gas film is advantageous for firearms owing to the efiicient sealing of the projectile in the barrel. The lubricant gas layer obtained also seems to form a protective layer for the portions of the inner barrel wall subject to particular attack by the corrosive explosion products. It may be possible that the sudden improvement of the life of firearm barrels obtainable by means of this method is not caused by the reduction of the losses due to sliding friction itself, but to the reduction of the detrimental effects of the usually high sliding friction, suchas wear and increased danger of erosion. I

What is claimed is:

1. A method of reducing the wear on the inner wall of weapon barrels caused by the passage of projectiles therethrough, comprising applying to the guiding surface portions of projectile having a melting point substantially equal or below the melting point of the inner barrel wall, a very thin deformable coating of a metal having a melting point higher than said guiding portions whereby material transfer from the coated guiding surfaces to the barrel walls is prevented.

2. A method according to claim ll wherein the melting point of the said guiding surface portions of the projectile is influenced by enriching with a foreign substance diffused therein.

3. A method according to claim 1 wherein the coating metal is selected from the group consisting of chromium, nickel and cobalt.

4. Guiding portions of projectiles comprising a base material of a metal having a melting point below that of the alloy of the inner barrel wall and having applied 'thereto a thin exterior protective coating of a higher melting metal having a higher resistance to wear, said coating being of a thickness sufficient to protect the surface zones of said guiding portions during one passage through the barrel but not of a thickness capable of increasing the deformation strength of said guiding portions.

5. Guiding portions of projectiles comprising a base material of a metal enriched with a substance to lower its melting point below that of the alloy of the inner barrel wall and having applied thereto a thin exterior protective coating of a higher melting metal having a higher resistance to wear, said coating being of a thickness sufiicient to protect the surface zones of said guiding portions during one passage through the barrel.

6. The combination of claim 4 wherein the ferrous driving bands are microporous are enriched with nitrogen and are coated with a thin film of a higher melting, more wear resistant metal, said film being of a thickness to protect the surface zones of said driving bands during one passage through the barrel.

7. A method of reducing the wear on the inner wall of weapon barrels caused by the passage of projectiles therethrough, comprising applying to the guiding surface portions of a projectile having a melting point substantially equal or below the melting point of the inner barrel wall, a very thin deformable coating of a metal having a melting point higher than said guiding portions, thecoating is of a metal which is readily deformable with the rifiing of the barrel, has a high wear resistance, a higher melting point than that of the gun barrel alloy or of the base material of the guiding portions of the projectile and is of a thickness suflicient to protect the surface zones of said guiding portions during one passage through the barrel.

8. A method according to claim 2 in which said enrichment is effected by heating said surface portions in an electric glow discharge in a gaseous or vaporous atmosphere containing saxid enriching substance 'until the surface is made microporous and enriched in such amount that the melting point of said surface zone is reduced to near or below the melting point of the inner barrel wall.

9. A method according to claim 8 in which said guiding surface portions are composed of ferrous material and are enriched with nitrogen.

References Cited by the Examiner UNITED STATES PATENTS 4/1959 Great Britain. 12/1960 Great Britain.

6/ 1956 Switzerland.

BENJAMIN A. BORCHELT, Primary Examiner.

R. F. STAHL, Assistant Examiner. 

1. A METHOD OF REDUCING THE WEAR ON THE INNER WALL OF WEAPON BARRELS CAUSED BY THE PASSAGE OF PROJECTILES THERETHROUGH, COMPRISING APPLYING TO THE GUIDING SURFACE PORTIONS OF PROJECTILE HAVING A MELTING POINT SUBSTANTIALLY EQUAL OR BELOW THE MELTING POINT OF THE INNER BARREL WALL, A VERY THIN DEFORMABLE COATING OF A METAL HAVING A MELTING POINT HIGHER THAN SAID GUIDING PORTIONS WHEREBY MATERIAL TRANSFER FROM THE COATED GUIDING SURFACES TO THE BARREL WALLS IS PREVENTED. 